Hi,

I have used 9mm diameter Rigid Gas Permeable contact lens for over
20 years with base curve of 7.8. Yesterday, a new optometrist tested
my eyes and said the 9mm diameter is too small and prescribe me
10mm. Isn't 10mm too big? She said my eyes is 9.5mm but she
wants larger like 10mm for more comfortable fit. After researching
in the net, I learnt that larger diameter can have poorer tear
exchange.
Now how do I know if the 10mm is optimal or poor for my tear
exchange?

Also she said my base curve is now 7.9. How do you calculate
changes in base curve and increase in optical powers (like 0.1mm
base curve increase corresponding to decrease in powers like
-1.0 diopters? What's the formula?

Thanks.

Pia